Prealloy for the production of cast iron and method for producing the prealloy



Patented July 15, 1952 PREALLOY FOR THE PRODUCTION OF CAST IRON AND METHOD FOR PRODUCING THE PREALLOY Lester C. Crome, West Alexandria, Ohio, assignor to The Dayton Malleable Iron Company, Dayton, Ohio, a corporation of Ohio No Drawing. Application July 18, 1949,

Serial No. 105,442

Claims. 1

This invention relates to cast iron, and more particularly to a new cast iron, and the production thereof, which when cast produces finished cast iron or castings which are markedly different in characteristics from the cast irons as heretofore known such as so-called gray iron, malleable iron and white iron.

One of the principal objects of this invention is to provide a molten iron mix which in the molten state is such that the addition of small quantities of selected materials, as in the ladle before pouring into the mold, will produce this new iron of characteristics widely different from the long and widely known gray irons, also from the white iron castings long produced to have such characteristics that upon heat treatment or annealing they will become the so-called malleable irons, and also from the malleableized irons which result from the annealing or heat treatment of white iron castings.

Another object of the invention is to produce such new iron, and castings of desired form, directly, as by the pouring into the mold with subsequent solidification on cooling, and without the necessity of the expensive annealing which is required to make white iron castings into the usual malleableized castings.

Still another object of the invention is to provide a method in the production of such molten iron mixes and the forming of castings thereof to produce the new iron product.

It is a further object of the invention to provide an alloy for addition to the molten ironmix to produce this new iron having the desired characteristics.

It is also an object to provide a simple and eflective method of producing such alloys in the desired proportion and of properly protecting the constituents of the alloy in the production thereof.

Other objects and advantages will be apparent from the appended description and the claims.

So-called gray iron, as castings of finished characteristics when removed from the mold, and malleable iron produced by making castings of a white iron mix and then subjecting the casting to the long and expensive annealing treatment have long been known in the iron foundry industry. It has also been long recognized that in the making of gray iron castings the constituents and the relative proportions thereof which are present in the molten iron mix (which may be controlled by determining the proportions which are admixed before melting to form the molten gray iron mix) must be such that when the molten gray iron is poured into the mold and is allowed to cool, most of the carbon which is present in the mix will separate so that in the finished casting it will be in fiat or flake-like form, of varying dimensions. This fiat or flakelike graphite carbon, produced by the presence of the constituents in such proportions that at least one of them has what is called a graphitizing effect to separate most of the carbon as the fiat or flake-like graphitic carbon, is universally recognized as being characteristic of so-called gray iron castings. Such a casting, in fracture, has an irregular surface which appears as of a definitely gray color, due in part at least to the efiect of the flake graphite with respect to the reflected light, which is characteristic; hence its designation as gray iron.

On the other hand, it is equally well recognized that for the production of malleable iron which has generally greater strength than gray iron and also is ductile and is capable of considerable elongation under tension or of bending, the castings must be produced from constituents which are such and the proportions of which are such, that when the molten iron mix is poured into the mold and allowed to cool the resulting casting will be free from the flake-like graphitic carbon described above in connection with gray iron. The presence of any appreciable quantity of flake-like graphitic carbon in the iron as cast will render a seemingly white iron casting useless for the production of malleable iron, as the graphitic carbon in malleable iron is that which is formed during the heat treatment from combined carbon, or iron carbides, and if graphitic carbon is in the casting as removed from the mold, in any appreciable quantity, the subsequent heat treatment or annealing will not change the inherent characteristics of the casting to give it those characteristics which are essential for so-called malleable iron. Su h a casting, free from graphitic carbon as castfin fracture appears white or a very silvery gray, and the appearance of the fracture of such a white iron casting is so markedly difierent from the appearance of the fracture of a gray iron casting, due to the differences in light reflection that the white or silvery gray appearance from such castings has led to the designation of white iron. Such castings, are so extremely hard with respect to the usual machining operations, etc, that they are produced (except perhaps for some special end use) only because the inherent characteristics are such that upon the proper heat treatment or annealing the iron carbides break down and form free carbon; but in such circumstances the characteristics of the casting cause the resulting graphitic carbon to appear as socalled nodules. That is, the usual malleable annealing operation causes a breaking down of the iron carbides to form free carbon but not in the form of the flat or flake-like graphite which occurs in gray iron castings. Generally the carbon or graphite as separated from the carbides during anneal of a white iron casting appears as so-called nodules or temper carbon, the carbon after such anneal being separated and distributed as generally spherical or nodular as observed under the microscope or in photomicrographs.

The present invention has to do with the production of a new form of iron in which the finished casting is made from an iron mix which would be generally close in constituents and proportions to the mixes which have long been used in the gray iron foundry industry. By the addi-- tion of small quantities of certain other constituents to the molten mix, an iron casting is produced which has free graphitic carbon appearing in the casting but such that there is substantially no flake-like graphitic carbon of typical gray iron described above formed while the casting is being made. The separated or graphitic carbon is in nodular form which in size and distribution and regularity of shape is comparable with the nodules of carbon in malleableized white iron.

This invention, therefore, has produced a new cast iron, which in its cast form and without any annealing or other treatment, has free, separated carbon but with the carbon in nodular form and as these nodules are small and discontinuous they interrupt the iron matrix which gives the real strength to the casting much less than is the case with ordinary gray cast iron with its flake-like graphitic carbon and therefore the castings as produced have much greater strength under the impact or shock test and also under the standard transverse test. The tensile strength of this new iron is much above that of ordinary gray iron castings and good grades of malleableized iron castings. As a fair comparison the tensile strength of this new iron is upward of 70,000 lbs. per square inch, and satisfactory castings have been produced with tensile strength of approximately 90,000 lbs. per square inch whereas the higher grade malleableized castings have tensile up to about 513,000-235,000 lbs. per square inch, and ordinary gray iron castings have tensile strengths varying widely from under 20,000 lbs. up to 45,000 lbs. per square inch. The iron, however, is not ductile or subject to elongation under tension as is the cast with malleableized iron nor has it any substantial capacity for bending, which is true, of course, of malleable iron which can be given a considerable bend without fracture or breaking. In this so-called shock or impact test, a test bar of iron has one end held in a vise, or some other equivalent mechanism, and the other end is struck with a pendulum in a precision machine for such impact testing, in which a free swinging pendulum of given weight and length is elevated to a predetermined height and released. The impact measurement is determined by a scale calibrated to show the foot pounds of energy absorbed to break the test casting. This new iron has a shock or impact test which is far in excess of that of a comparable cross-section gray iron casting. The impact test on a comparable crosssection malleableized white iron casting may be of no import, because of the bending characteristics of malleable iron.

Thus an entirely new iron is made available in cast form, of these characteristics, which gives it great superiority over ordinary gray iron in the respects mentioned, in that it has a high shock or impact test and therefore can withstand shocks or blows in use which would be completely destructive of gray iron. It also has characteristics in certain respects which are superior to the malleableized white iron casting in that the greater tensile strength as stated above and the impact and transverse strength of the iron permits it to withstand shocks which might cause bending or distortion of a malleableized casting.

In the practicing of the invention it has been found that small proportions of magnesium, when introduced into a molten pig iron mix having constitutents within the range of proportion set out below, will result in the production of castings, which when completed and taken from the mold, will have the nodular form of graphitlc carbon and with the various characteristics above referred to. The character of magnesium is such, however, that it cannot safely be added as metallic magnesium to the molten iron mix a violent reactions will occur. In fact, in most forms of alloyed magnesium its reactivity is so great that it is too dangerous to use. However, if the magnesium is alloyed with copper, the resulting alloy can be safely used in the practicing of the present invention. The copper does not adversely affect the formation of the nodules of graphitic carbon which are produced by the action of the magnesium and it is comparatively cheap and therefore does not materially affect the cost of the cast ing.

Very satisfactory nodular graphite castings of the new iron have been produced using a copper magnesium alloy containing of copper and 10% of magnesium. While such an alloy is still quite active in the molten iron due to the presence of magnesium, it can be readily prepared and safely used in the practicing of the invention. Copper magnesium alloys within the range of copper 90 to and magnesium 5 to 10% have been found satisfactorily useable, such alloy being added originally in the range of about .1% to 2% of magnesium on the mix. Additional alloy may be added for longer pouring periods as set out below.

While magnesium as thus allowed with copper gives highly satisfactory results, and magnesium seems to have a great activity or effect in causing the formation of the nodules of carbon, its great activity presents the problem of more careful handling than is the case when magnesium is alloyed with other materials hereinafter described. The use of an alloy consisting predominately of copper with relatively small quantities of magnesium and misch metal has been found thus far to give highly satisfactory results in operation, having in mind the various factors mentioned above. Such an alloy containing approximately 85% copper, 10% magnesium and 5% misch metal gives a new iron casting with the desirable characteristics referred to and with the nodules of graphitic carbon as formed in the iron while the casting is being produced in the mold being not only nodular but of a high degree of uniformity of dimensions of the nodules.

A coppe -misch metal, magnesium alloy has been found satisfactorily usable within the ranges:

Per cent Copper 63-90 Magnesium 30-7 Misch metal '7-3' and satisfactory results have been secured with the addition of about 1% to 2% of such alloy, depending upon the responsiveness of the iron mix to the new, nodular or spherical precipitation material.

In the preparation of the alloy for use in accordance with the present invention, it is important to observe proper care and to carry out the operation under properly controlled conditions, in order to avoid either igniting the highly combustible magnesium material, or undue loss of magnesium as a result of oxidation or the like. It has been found that the alloy may be prepared without objectionable loss in the following manner. The magnesium is first heated in a suitable vessel, such as a crucible, to a temperature at least suilicient to cause it to soften or partly melt, it having been found that it is ordinarily not necessary to actually reduce the metal to a truly molten condition. A suitable temperature for this purpose is about 1200 F. Thereafter the copper is heated to a molten state, at about its melting temperature, satisfactorily about 2000 F. In the alloy specifically referred to herein for the cast iron field to produce the nodular or spherical graphitic iron as cast, the copper is largely in excess and for satisfactorily producing the alloy with the substantial proportions of magnesium referred to, the molten copper is then added to the vessel containing the softened magnesium by pouring the copper into or onto the magnesium. The greater heat of the copper causes the magnesium to melt and a homogeneous mixture of the two metals thus results without too great loss of magnesium, the molten copper alloying with the magnesium, and the resulting characteristics of the mixture are such that it becomes quite fluid even at temperatures somewhat below the melting temperature of the copper.

It has been found desirable to reduce the temperature of the mixture as quickly as possible, and for this purpose it is preferred to chill the mixture such as by pouring it into molds which will bring about a rapid reduction in temperature. Where it is desired to also incorporate misch metal into the mixture or alloy, that may be done by adding the same in solid form to the molten coppermagnesium and in the proportion necessary to produce the desired content in the finished alloy. As its melting range is well below that of the copper it may be added in solid form, in chunks of such size as will melt or go into solution readily and mix as added so long as the quantity and temperature of the copper and magnesium molten mix are adequate. While the misch metal appears to develop a protective effect on the magnesium it is also desirable to follow the same practice in chilling the mixture.

The foregoing procedure is quite satisfactory where the mixture or resulting alloy does not contain more than about magnesium. However where an alloy of higher magnesium content,

up to the 30% magnesium, is desired, the procedure is preferably somewhat varied as follows. The magnesium is first melted, and the desired amount of misch metal is then added to the molten magnesium in solid form, which quickly forms a mixture or molten solution in which the misch metal appears to develop the protecting effect upon the magnesium. As a result, the molten copper may thereafter be added to the mixture, and even though magnesium is present in an amount substantially above 10%, this method provides for proper formation of the composite alloy without either igniting the magnesium or objectionably oxidizing or vaporizing the same.

The misch metal referred to is available commercially, the mixture being generally uniform and a lay-product of the production of thorium, and its commercial composition is approximately within the ranges set out below:

Per cent Cerium 45 Lanthanum 25 Neodynium and Prazeodymium 15 Samarium 10 An iron mix containing constituents within the following percentage ranges:

Per cent Carbon 3.0 -4.3 Silicon 2.0 -4.0 Manganese 0.4 2.0 Phosphorus 0.01-04 Sulphur Less than 0.04

has been found to satisfactorily produce this new iron when the copper magnesium alloy or the copper magnesium misch metal alloy in the proportions set out above is added to the molten mix in the ladle before pouring It has also been found that when magnesium in some one of the alloy forms referred to, is added to the molten metal there is a comparatively short time interval during which sufficient of the magnesium or other alloy constituents such as misch metal will remain available in the molten metal to have the effect of controlling to cause the nodules of graphite carbon to be separated or precipitated in the coolin metal in the mold (or from the high temperature solid solution metal in the mold). Probably due to oxidation, or perhaps reaction of magnesium or the misch metal or both with some other materials present, the quantity introduced in the molten mix and effective to form the nodular graphitic carbon is decreased rather rapidly, the time varying inversely with respect to the temperature of the molten iron in the ladle. In practicable operations producing castings of thi new iron, it has been found that the magnesium constituent of the magnesium, copper alloy and the magnesium and misch metal constituents of the copper, magnesium, misch metal alloy, in the small percentage ranges specified as effective to produce nodular graphitic carbon, will remain as such in sufficient quantity to produce the desired results for a period from about 7 to 13 minutes, after which time the production of the nodular graphitic carbon no longer occurs. If either of the above disclosed alloys is introduced into a ladle of molten iron which will be poured under such circumstances that the vitalizing reactions will not be terminated within the short period of pouring, the resulting castings will have the de sired characteristics of this new iron.

It has been found, however, that if a longer 7 period than the 7 to 13 minutes referred to is allowed to elapse before the molten iron is all poured into the mold and is in such condition of cooling that the nodular graphite is not produced, the adding of small additional quantities 4 of the magnesium, copper, or the copper, magin the molten iron against graphitic precipitation.

When the small amounts of such alloys as referred to above are introduced into the molten iron mix the molten iron should be poured within a period of from about 7 to 13 minutes and unless this is done, it is found that the amount of effective alloy material that is available to cause nodular carbon to appear is diminished so that the alloy is no longer effective to form nodular carbon as desired. It the amount of such alloys added to the molten mix is increased too much it not only has a stabilizing efiect in the molten iron but also inhibits the breaking down of the carbides after the iron becomes solid which in turn may inhibit the formation of nodular carbon.

It has been found however that when additional amounts of these alloys are added into the ladle to prolong the pouring period, the inhibiting effects against the carbides breaking down in the solidified metal can be overcome provided a small percentage of an active graphitiz-ing agent is added along with such alloys. For example satisfactory results have been secured where the amount of the alloy which is added is increased after this 7 to 13 minute period by the addition of about .5% on the mix, and at the same time 0.20% of a strong graphitizing agent such as calcium silicide was added, and under these conditions it was possible to increase the time of pouring and at the same time maintaining the stabilizing effect against graphitic precipitation and allowing the carbides to separate and form nodular carbon. Not only does the addition of the nodular forming metal or metals or alloys thereof build up the nodule forming charactristics to approximately the original effectiveness but when added along with a small percentage of the graphitizing agent the period during which this nodule forming graphitization will still take place is quite considerably increased, to as much as the 7 to 13 minutes of the original addition which in most cases will be ample for commercial foundry practices. To assure ample time for satisfactory operations over 20 to 26 minutes, however, it may be found desirable to add a second addition of about 0.5% of the alloy materials, and a second corresponding addition of about 0.2% of a strong graphitizing agent and a satisfactory casting of the nodular containing iron will thus be assured within the maximum time mentioned and without inhibiting the decomposition of the iron carbides.

This application is a continuation-in-part of my copending application, Lester C. Crome, Serial No. 41,906, filed July 31, 1948, and reference is made to the Amendment Before Ofiice Action with supporting oath, executed and filed of even date with said copending application and form ing a part thereof.

,What is claimed is:

1. For use in the producing of iron castings of the character described from a molten gray iron mix by adding to said mix before pouring a predetermined limited amount of an alloy of magnesium, misch metal and copper, such that upon pouring said molten mix into a mold, and then removing the casting from the mold as a finished casting, said casting will contain its graphitic carbon in spherical or nodular form, without subsequent annealing, and substantially free of the usual flake-like graphitic carbon of gray iron castings; an alloy which goes into solution when added to the molten gray iron mix as a ladle addition and which comprises approximately 10% magnesium, 5% misch metal and copper and which is effective to cause precipitation of the graphitic carbon in said nodular or spherical form.

2. For use in the producing of iron castings of the character described from a molten gray iron mix by adding to said mix before pouring a predetermined limited amount of an alloy of magnesium, misch metal and copper, such that upon pouring said molten mix into a mold, and then removing the casting from the mold as a finished casting, said casting will contain its graphitic carbon in spherical or nodular form, without subsequent annealing, and substantially free of the usual flake-like graphitic carbon of gray iron castings, an alloy which goes into solution when added to the molten gray iron mix as a ladle addition and comprising approximately 7 to 30% magnesium, 3 to 7% misch metal and 63 to copper, and which is eiiective to cause precipitation of the graphitic carbon in said nodular or spherical form.

3. For use in the producing of iron castings of the character described from a molten gray iron mix by adding to said mix before pouring a predetermined limited amount of an alloy of magnesium and misch metal, such that upon pouring said molten mix into a mold, and then removing the casting from the mold as a finished casting, said casting will contain its graphitic carbon in spherical or nodular form without subsequent annealing and substantially free of the usual flakelike graphitic carbon of gray iron castings; an alloy which goes into solution when added to the molten gray iron mix as a ladle addition and comprising as essential constituents about 7 to 15% magnesium and about 3% to 7% misch metal admixed with a residue consisting of a carrying constituent primarily of copper, and which is efiective to cause precipitation of the graphitic carbon in said nodular or spherical form.

4. A preformed alloy for addition in a predetermined small amount to a molten gray iron mix to produce an iron in which as cast the precipitated carbon is present as free graphitic carbon in generally spherical or nodular form and generally uniform in distribution, said alloy containing as essential constituents about 7% to 15% magnesium and about 3% to 7 misch metal admixed with a residue consisting of a carrier constituent primarily of copper.

5. The process of producing an alloy of the character described for addition to a molten gray iron mix which comprises heating magnesium to its softening point, heating copper to a substantially molten state, adding said molten copper to said softened magnesium, and incorporating misch metal into the resulting magnesium copper mixture to provide for said alloy containing approximately 7% to 30% magnesium, 3% to 7% misch metal, and 63% to 90% copper.

6. The process of producing an alloy of the character described containing less than approximately magnesium for addition to a molten gray iron mix which comprises heating magnesium to its softening point, heating copper to a substantially molten state, adding said molten copper to said softened magnesium, adding misch metal in solid form to said mixture of copper and magnesium, and subjecting said mixture to chilling to reduce the loss of magnesium therefrom.

7. The process of producing an alloy of the character described containing more than approximately 10% magnesium for addition to a molten gray iron mix which comprises melting the magnesium, adding misch; metal to said melted magnesium as an oxidation inhibitor for said magnesium, heating copper to a substantially molten state, and adding said molten copper to said mixture of magnesium and misch metal.

8. A process of producing an alloy of the character described for addition to a gray iron mix which comprises heating magnesium to its softening point, heating copper to a substantially molten state, adding said molten copper to said softened magnesium in proportion to form a mixture which contains up to about 30% magnesium, thereafter adding misch metal to said mixture, and chilling said mixture to reduce the loss of magnesium therefrom.

9. The process of producing an alloy of the character described for addition to a molten gray iron mix which comprises heating magnesium to its softening point, adding misch metal thereto in proportion to form about 3% to 10% of said alloy, heating copper to a substantially molten state, adding said molten copper to said mixture of magnesium and misch metal in proportion such that the resulting alloy contains in excess of about 10% and up to about magnesium.

10. For use in the producing of iron castings of the character described from a molten gray iron mix by adding to said mix before pouring a predetermined limited amount of an alloy of magnesium, misch metal and copper, such that upon pouring said molten mix into a mold, and then removing the casting from the mold as a finishing casting, said casting will contain its graphitic carbon in spherical or nodular form, without subsequent annealing, and substantially free of the usual flake-like graphitic carbon of gray iron castings; an alloy which goes into solution when added to the molten gray iron mix as a ladle addition and Which comprises approximately 20% magnesium, 5% misch metal and 75% copper and which is eiiective to cause precipitation of the graphitic carbon in said nodular or spherical form.

LESTER C. CROME.

file of this patent:

UNITED STATES PATENTS 

2. FOR USE IN THE PRODUCING OF IRON CASTINGS OF THE CHARACTER DESCRIBED FROM A MOLTEN GRAY IRON MIX BY ADDING TO SAID MIX BEFORE POURING A PREDETERMINED LIMITED AMOUNT OF AN ALLOY OF MAGNESIUM, MISCH METAL AND COPPER, SUCH THAT UPON POURING SAID MOLTEN MIX INTO A MOLD, AND THEN REMOVING THE CASTING FROM THE MOLD, AND FINISHED CASTING, SAID CASTING WILL CONTAIN ITS GRAPHITIC CARBON IN SPHERICAL OR NODULAR FORM, WITHOUT SUBSEQUENT ANNEALING, AND SUBSTANTIALLY FREE OF THE USUAL FLAKE-LIKE GRAPHITIC CARBON OF GRAY IRON CASTINGS, AN ALLOY WHICH GOES INTO SOLUTION WHEN ADDED TO THE MOLTEN GRAY IRON MIX AS A LADLE ADDITION AND COMPRISING APPROXIMATELY 7 TO 30% MAGNESIUM, 3 TO 7% MISCH METAL AND 63 TO 90% COPPER, AND WHICH IS EFFECTIVE TO CAUSE PRECIPITATION OF THE GRAPHITIC CARBON IN SAID NODULAR OR SPHERICAL FORM. 